Vascular but not cardiac remodeling is associated with superoxide production in angiotensin II hypertension.

OBJECTIVE

Angiotensin (Ang) II increases reactive oxygen species (ROS), decreases nitric oxide (NO) bioavailability and promotes cardiovascular remodeling. ROS have been identified as critical second messengers of the trophic responses by Ang II. In rats with Ang II-induced hypertension, we investigated the role of ROS in cardiac hypertrophy as well as the remodeling of aortas and mesenteric (resistance) arteries.

METHODS

Sprague-Dawley rats received Ang II (0.7 mg/kg per day by mini-pump, n = 7) or vehicle (n = 7) for 5 days. Endothelium-dependent relaxation to acetylcholine (EDR) in aortas was determined in organ baths and in mesenteric resistance vessels in a pressurized myograph. Superoxide (O2) production was measured by lucigenin chemiluminescence, laser-confocal fluorescence microscopy (LCM) and NADPH oxidase assay.

RESULTS

Ang II-treated rats developed hypertension (183 +/- 3 versus 138 +/- 4 mmHg, P < 0.05), increased aortic O2 (50%), aortic hypertrophy (12%) and impaired EDR. Mesenteric arteries manifested impaired EDR, increased NADPH oxidase activity (356%) and eutrophic inward remodeling (decreased lumen diameter and increased wall/lumen ratio). However, although Ang II-treated rats developed cardiac hypertrophy (13%), this was not accompanied by an increase in cardiac O2, as measured by lucigenin, LCM or NADPH oxidase assay. On the other hand, cardiac calcineurin, a molecule that promotes cardiac hypertrophy linked to Ang II, was increased by 40% (52 +/- 8 versus 33 +/- 5 pmol/min per mg protein, P < 0.05).

CONCLUSION

These studies demonstrate that the role of ROS in Ang II-induced vascular remodeling differ across vascular territories. Although in conduit and resistance vessels, vascular hypertrophy and endothelial dysfunction are linked to increased ROS production, cardiac hypertrophy is not. Instead, cardiac hypertrophy is associated, at least in part, with an increase in calcineurin. These studies unveil novel mechanisms that may play an important role in the pathogenesis of cardiac and vascular injury in hypertension.